Isolation structure for deflectable nanotube elements

ABSTRACT

Nanotube-based switching elements and logic circuits. Under one embodiment of the invention, a switching element includes an input node, an output node, a nanotube channel element having at least one electrically conductive nanotube, and a control electrode. The control electrode is disposed in relation to the nanotube channel element to controllably form an electrically conductive channel between the input node and the output node. The channel at least includes said nanotube channel element. The output node is constructed and arranged so that channel formation is substantially unaffected by the electrical state of the output node. Under another embodiment of the invention, the control electrode is arranged in relation to the nanotube channel element to form said conductive channel by causing electromechanical deflection of said nanotube channel element. Under another embodiment of the invention, the output node includes an isolation structure disposed in relation to the nanotube channel element so that channel formation is substantially invariant from the state of the output node. Under another embodiment of the invention, the isolation structure includes electrodes disposed on opposite sides of the nanotube channel element and said electrodes produce substantially the same electric field. Under another embodiment of the invention, a Boolean logic circuit includes at least one input terminal and an output terminal, and a network of nanotube switching elements electrically disposed between said at least one input terminal and said output terminal. The network of nanotube switching elements effectuates a Boolean function transformation of Boolean signals on said at least one input terminal. The Boolean function transformation includes a Boolean inversion within the function, such as a NOT or NOR function.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Pat. Apl., Ser. No. 60/494,889, filed on Aug. 13, 2003,entitled Nanoelectromechanical Nanotube-Based Logic, which isincorporated herein by reference in its entirety.

This application is related to the following references:

-   -   U.S. Pat. Apl., Ser. No. not yet assigned, filed on date even        herewith, entitled Nanotube-Based Switching Elements; [Nan-31]    -   U.S. Pat. Apl., Ser. No. not yet assigned, filed on date even        herewith, entitled Nanotube-Based Switching Elements and Logic        Circuits; [Nan-78]    -   U.S. Pat. Apl., Ser. No. not yet assigned, filed on date even        herewith, entitled Nanotube-Based Switching Elements with        Multiple Controls; [Nan-45]    -   U.S. Pat. Apl., Ser. No. not yet assigned, filed on date even        herewith, entitled Circuits Made from Nanotube-Based Switching        Elements with Multiple Controls; [Nan-80]    -   U.S. Pat. Apl., Ser. No. not yet assigned, filed on date even        herewith, entitled Nanotube Device Structure and Methods of        Fabrication. [Nan-46]

BACKGROUND

1. Technical Field

The present application generally relates to nanotube switching circuitsand in particular to nanotube switching circuits that use nanotubes toform a conductive channel of the switch and that may be interconnectedinto larger circuits, such as Boolean logic circuits.

2. Discussion of Related Art

Digital logic circuits are used in personal computers, portableelectronic devices such as personal organizers and calculators,electronic entertainment devices, and in control circuits forappliances, telephone switching systems, automobiles, aircraft and otheritems of manufacture. Early digital logic was constructed out ofdiscrete switching elements composed of individual bipolar transistors.With the invention of the bipolar integrated circuit, large numbers ofindividual switching elements could be combined on a single siliconsubstrate to create complete digital logic circuits such as inverters,NAND gates, NOR gates, flip-flops, adders, etc. However, the density ofbipolar digital integrated circuits is limited by their high powerconsumption and the ability of packaging technology to dissipate theheat produced while the circuits are operating. The availability ofmetal oxide semiconductor (“MOS”) integrated circuits using field effecttransistor (“FET”) switching elements significantly reduces the powerconsumption of digital logic and enables the construction of the highdensity, complex digital circuits used in current technology. Thedensity and operating speed of MOS digital circuits are still limited bythe need to dissipate the heat produced when the device is operating.

Digital logic integrated circuits constructed from bipolar or MOSdevices do not function correctly under conditions of high heat orextreme environments. Current digital integrated circuits are normallydesigned to operate at temperatures less than 100 degrees centigrade andfew operate at temperatures over 200 degrees centigrade. In conventionalintegrated circuits, the leakage current of the individual switchingelements in the “off” state increases rapidly with temperature. Asleakage current increases, the operating temperature of the devicerises, the power consumed by the circuit increases, and the difficultyof discriminating the off state from the on state reduces circuitreliability. Conventional digital logic circuits also short internallywhen subjected to extreme environments they may generate electricalcurrents inside the semiconductor material. It is possible tomanufacture integrated circuits with special devices and isolationtechniques so that they remain operational when exposed to extremeenvironments, but the high cost of these devices limits theiravailability and practicality. In addition, such digital circuitsexhibit timing differences from their normal counterparts, requiringadditional design verification to add protection to an existing design.

Integrated circuits constructed from either bipolar or FET switchingelements are volatile. They only maintain their internal logical statewhile power is applied to the device. When power is removed, theinternal state is lost unless some type of non-volatile memory circuit,such as EEPROM (electrically erasable programmable read-only memory), isadded internal or external to the device to maintain the logical state.Even if non-volatile memory is utilized to maintain the logical state,additional circuitry is necessary to transfer the digital logic state tothe memory before power is lost, and to restore the state of theindividual logic circuits when power is restored to the device.Alternative solutions to avoid losing information in volatile digitalcircuits, such as battery backup, also add cost and complexity todigital designs.

Important characteristics for logic circuits in an electronic device arelow cost, high density, low power, and high speed. Conventional logicsolutions are limited to silicon substrates, but logic circuits built onother substrates would allow logic devices to be integrated directlyinto many manufactured products in a single step, further reducing cost.

Devices have been proposed which use nanoscopic wires, such assingle-walled carbon nanotubes, to form crossbar junctions to serve asmemory cells. (ee WO 01/03208, Nanoscopic Wire-Based Devices, Arrays,and Methods of Their Manufacture; and Thomas Rueckes et al., “CarbonNanotube-Based Nonvolatile Random Access Memory for MolecularComputing,” Science, vol. 289, pp. 94-97, 7 July, 2000.) Hereinafterthese devices are called nanotube wire crossbar memories (NTWCMs). Underthese proposals, individual single-walled nanotube wires suspended overother wires define memory cells. Electrical signals are written to oneor both wires to cause them to physically attract or repel relative toone another. Each physical state (i.e., attracted or repelled wires)corresponds to an electrical state. Repelled wires are an open circuitjunction. Attracted wires are a closed state forming a rectifiedjunction. When electrical power is removed from the junction, the wiresretain their physical (and thus electrical) state thereby forming anon-volatile memory cell.

U.S. Patent Publication No. 2003-0021966 discloses, among other things,electromechanical circuits, such as memory cells, in which circuitsinclude a structure having electrically conductive traces and supportsextending from a surface of a substrate. Nanotube ribbons that canelectromechanically deform, or switch are suspended by the supports thatcross the electrically conductive traces. Each ribbon comprises one ormore nanotubes. The ribbons are typically formed from selectivelyremoving material from a layer or matted fabric of nanotubes.

For example, as disclosed in U.S. Patent Publication No. 2003-0021966, ananofabric may be patterned into ribbons, and the ribbons can be used asa component to create non-volatile electromechanical memory cells. Theribbon is electromechanically-deflectable in response to electricalstimulus of control traces and/or the ribbon. The deflected, physicalstate of the ribbon may be made to represent a corresponding informationstate. The deflected, physical state has non-volatile properties,meaning the ribbon retains its physical (and therefore informational)state even if power to the memory cell is removed. As explained in U.S.Patent Publication No. 2003-0124325, three-trace architectures may beused for electromechanical memory cells, in which the two of the tracesare electrodes to control the deflection of the ribbon.

The use of an electromechanical bi-stable device for digital informationstorage has also been suggested (c.f. US4979149: Non-volatile memorydevice including a micro-mechanical storage element).

The creation and operation of bi-stable, nano-electro-mechanicalswitches based on carbon nanotubes (including mono-layers constructedthereof) and metal electrodes has been detailed in a previous patentapplication of Nantero, Inc. (U.S. Pat. Nos. 6,574,130, 6,643,165,6706402; U.S. Patent Apl. Ser. Nos. 09/915,093, 10/033,323, 10/033,032,10/128,117, 10/341,005, 10/341,055, 10/341,054, 10/341,130, 10/776,059,and 10/776,572, the contents of which are hereby incorporated byreference in their entireties).

SUMMARY

The present invention provides isolation structures for deflectablenanotube elements.

Under another aspect of the invention, an isolation structure for adeflectable nanotube element includes a pair of electrodes disposed onopposite sides of a nanotube element. At least one of the pair ofelectrodes is an output terminal, and the pair produces substantiallythe same electric field on the nanotube element.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawing,

FIGS. 1A-1C illustrate cross-sectional views of a nanotube switchingelement of certain embodiments in two different states and include alayout view of such element;

FIGS. 2A and 2B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view;

FIGS. 3A and 3B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view;

FIGS. 4A and 4B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view;

FIGS. 5A and 5B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view;

FIGS. 6A and 6B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view;

FIGS. 7A and 7B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view;

FIGS. 8A and 8B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view;

FIGS. 9-11C show the layout and operation of an exemplary invertercircuit;

FIGS. 12A-16C show the layout and operation of an exemplary NOR circuit;and

FIGS. 17A and 17B illustrate a ring oscillator according to certainembodiments.

DETAILED DESCRIPTION

Preferred embodiments of the invention provide switching elements inwhich a nanotube-based channel may be controllably formed, under theinfluence of a control node, so that a signal may be transferred to anoutput node. The transferred signal may be a varying signal or areference signal, depending on the manner in which the switching elementis utilized and arranged. Preferred embodiments provide an isolationstructure so that such signal transfer and the switching element'soperation is substantially invariant to the output state. For example,the output node may float and/or be tied to other electrical componentsand the circuit will operate in a predictable switch-like manner.Consequently, the switching elements may be formed into larger circuits,such as Boolean logic circuits. Under some embodiments, the switchingelements are used as complementary circuitry.

FIGS. 1A and 1B are cross-sectional views of an exemplary nanotubeswitching element and FIG. 1C is a layout view of such element. Theswitching element 100 includes a control electrode 101, a nanotubechannel element 103, an output node 102 (in turn including outputelectrodes 102 a and 102 b), supports 104 and signal electrode 105.

In this embodiment, the nanotube channel element 103 is made of a porousfabric of nanotubes, e.g., single walled carbon nanotubes. In preferredembodiments, each nanotube has homogenous chirality, being either ametallic or semiconductive species. The fabric however may contain acombination of nanotubes of different species, and the relative amountsare preferably tailorable, e.g., fabrics with higher concentrations ofmetallic species. The element 103 is lithographically defined to apredetermined shape, as explained in the patent references incorporatedby reference herein. The nanotube channel element of preferredembodiments is suspended by insulative supports 104 in spaced relationto the control electrode 101 and the output electrodes 102 a,b. Thenanotube channel element 103 is held to the insulating supportstructures 104 by friction. In other embodiments, the nanotube channelelement 103 may be held by other means, such as by anchoring thenanofabric to the insulating support structures using any of a varietyof techniques. In this arrangement, the spacing between channel element103 and control electrode 101 is larger than the spacing between channelelement 103 and output electrodes 102 a,b. In certain preferredembodiments, the articles include substantially a monolayer of carbonnanotubes. In certain embodiments the nanotubes are preferred to besingle-walled carbon nanotubes. Such nanotubes can be tuned to have aresistance between 0.2-100 kOhm/□ or in some cases from 100 kOh/□ to 1GOhm/□.

Signal electrode 105 is in electrical communication with channel element103. In the preferred embodiment, the electrode 105 is in fixed,permanent contact with the channel element 103.

Specifically, the nanotube channel element may be coupled to anothermaterial (such as signal electrode 105) by introducing a matrix materialinto the spaces between nanotubes in a porous nanofabric to form aconducting composite junction, as described in the patent referencesincorporated herein. Electrical and mechanical advantages may beobtained by using such composite junctions and connections. In oneexample, a conducting material is deposited onto the nanofabric and isallowed to penetrate into the spaces within the porous nanofabric, thusforming an improved electrical connection to the nanofabric and reducescontact resistance in the article. In another example, an insulatingmaterial is deposited onto the nanofabric and is allowed to penetrateinto the spaces within the porous nanofabric, thus forming an improvedmechanical pinning contact that increases resistance to strain in thearticle (prevent nanotube slipping).

Evaporated or spin-coated material such as metals, semiconductors orinsulators—especially silicon, tungsten, titanium, silicon oxide,aluminum oxide or polyimide—may be used to increase the pinningstrength. The friction interaction can be increased through the use ofchemical interactions, including covalent bonding through the use ofcarbon compounds such as pyrenes or other chemically reactive species.See R. J. Chen et al., “Noncovalent Sidewall Functionalization ofSingle-Walled Carbon Nanotubes for Protein Immobilization,” J. Am. Chem.Soc., vol. 123, pp. 3838-39 (2001), and Dai et al., Appl. Phys. Lett.,vol. 77, pp. 3015-17 (2000), for exemplary techniques for pinning andcoating nanotubes by metals. See also WO 01/03208 for techniques.

In preferred embodiments, control electrode 101 is made of a conductivematerial portion 101 b covered with an insulator portion 101 a on thesurface facing nanotube channel element 103. It is insulated so there isno electrical connection between the nanotube fabric of the nanotubechannel element and the conductive portion 101 b of electrode 101, whenthe channel element 103 is deflected as shown in FIG. 1B. In this way,any signal on channel element 103 is transferred to output node 102.

Output node 102 has two electrodes 102 a,b on opposite sides of thenanotube channel element 103. In the state shown in FIG. 1A, thedistance between each electrode and the channel element 103 isapproximately the same. However, in this embodiment the distance betweenthe output electrode and the channel element 103 is smaller than thedistance between the channel element 103 and the control electrode 101.The upper electrode 102 b is part of an upper structure. The lowerelectrode 102 a in this embodiment also serves as the output node fromwhich the signal may be connected to other circuit elements. In apreferred embodiment, the two electrodes 102 a,b are electricallyconnected so that they are at substantially the same voltage and createsubstantially the same electrostatic force (though in oppositedirections) on the nanotube channel element 103.

Under certain embodiments, input, control, and output electrodes aretypically in the range of 50 to 200 nm wide. Control electrode oxidethickness is in the range of 5 to 30 nm. Supports are typically in therange of 50 to 200 nm. The suspended length of the nanotube element(between pinning supports) is typically in the range of 100 to 300 nm.Nanotube element fabric layer thickness is on the order of 0.5 to 3 nm(for SWNTs). The insulator surface of the control electrode is typically5 to 30 nm. The output electrode(s) to nanotube spacing is typically 5to 30 nm, for example. For volatile operation, the ratio of suspendednanotube length to the gap between the control electrode insulatorsurface and the nanotube element is typically 5 to 1. This, or anothersuitable ratio, is selected to ensure that the restoring mechanicalforce of the nanotube element exceeds the van der Waals forces on thenanotube element.

The nanotube switching element 100 operates in the following way. Ifsignal electrode 105 and control electrode 101 have a potentialdifference that is sufficiently large (via respective signals on theelectrodes), the relationship of signals will create an electrostaticforce F1 that is sufficiently large to cause the suspended, nanotubechannel element 103 to deflect into mechanical contact with electrode101. (This aspect of operation is described in the incorporated patentreferences.) This deflection is depicted in FIG. 1B. The attractiveforce F1 stretches and deflects the nanotube fabric of channel element103 until it contacts the insulated region 101 a of the controlelectrode 101. The nanotube channel element is thereby strained, andthere is a restoring tensil force, dependent on the geometricalrelationship of the circuit, among other things.

By using appropriate geometries of components, the switching element 100then attains the closed, conductive state of FIG. 1B in which thenanotube channel 103 mechanically contacts the control electrode 101 andalso output electrode 102 a. Since the control electrode 101 is coveredwith insulator 101 a (and therefore does not electrically connect[short] the signal on channel element 103 with the control signal oncontrol element 101 b) any signal on electrode 105 is transferred fromthe electrode 105 to the output electrode 102 a via the nanotube channelelement 103. The signal on electrode 105 may be a varying signal, afixed signal, a reference signal, a power supply line, or ground line.The channel formation is controlled via the signal applied to thecontrol electrode 101. Specifically the signal applied to controlelectrode 101 needs to be sufficiently different in relation to thesignal on electrode 105 to create the electrostatic force to deflect thenanotube channel element to cause the channel element 103 to deflect andto form the channel between electrode 105 and output electrode 102 a.

In contrast, if the relationship of signals on the electrode 105 andcontrol electrode 101 is insufficiently different, then the nanotubechannel element 103 is not deflected and no conductive channel is formedto the output electrode 102 a. Instead, the channel element 103 floats.This floating state is shown in FIG. 1A. The nanotube channel element103 has the signal from electrode 105 but this signal is not transferredto the output node 102. Instead, the state of the output node 102depends on whatever circuitry it is connected to and the state of suchcircuitry. The state of output node 102 in this regard floats and isindependent of the switching element 100.

If the voltage difference between the control electrode 101 and thechannel element 103 is removed, the channel element 103 returns to thenon-elongated state (see FIG. 1A), and the electrical connection or pathbetween the electrode 105 to the output node 102 is opened. The outputvoltage on the output electrode 102 a,b is of opposite polarity to thatof the control electrode 101 when a channel is formed. When there is noconnection, or channel, between the electrode 105 and the outputelectrode 102 a, the output node 102 may be at any voltage with respectto the channel element 103, the control electrode 101, and the signalelectode 105.

The output node 102 is constructed to include an isolation structure inwhich the operation of the channel element 103 and thereby the formationof the channel is invariant to the state of the output node 102. Sincein the preferred embodiment the channel element is electromechanicallydeflectable in response to electrostatically attractive forces, afloating output node 102 in principle could have any potential.Consequently, the potential on an output node may be sufficientlydifferent in relation to the state of the channel element 103 that itwould cause deflection of the channel element 103 and disturb theoperation of the switching element 100 and its channel formation; thatis, the channel formation would depend on the state of an unknownfloating node. In the preferred embodiment this problem is addressedwith an output node that includes an isolation structure to prevent suchdisturbances from being caused.

Specifically, the nanotube channel element 103 is disposed between twooppositely disposed electrodes 102 a,b of equal potential. Consequently,there are equal but opposing electrostatic forces F2 and F3 that resultfrom the voltage on the output node. Because of the equal and opposingelectrostatic forces, the state of output node 102 cannot cause thenanotube channel element 103 to deflect regardless of the voltages onoutput node 102 and nanotube channel element 103. Thus, the operationand formation of the channel is made invariant to the state of theoutput node.

FIGS. 2A and 2B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view. In this embodiment the gapdimensions between the channel element 103 and electrodes aresubstantially the same. Moreover the control electrode 101 and theoutput electrode 102 a are separated in part by insulative material 206.

FIGS. 3A and 3B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view. This embodiment is similarto the embodiment of FIG. 2 except that it includes another signalelectrode 306 connected to the nanotube channel element 103. This extraelectrode reduces the effective resistance.

FIGS. 4A and 4B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view. This embodiment is similarto that of FIGS. 3A and 3B, except that in this embodiment electrode 102b is replaced with electrode 402 b that is narrower. This allows closerplacement of signal electrode 306. The smaller electrode 402 b will havea smaller electric field affect on the nanotube channel element 103 allother things being equal. If necessary the electric field effect may betailored in other ways, e.g., altering the gap distance betweenelectrode 402 b and channel element 103.

FIGS. 5A and 5B show an alternative embodiment of a nanotube switchingelement in cross section view and plan view. This embodiment is similarto that of FIGS. 1A and 3A. It has the extra signal electrode 306 likethat of FIG. 3A along with insulator 206, and it also has different gapdimensions for the control electrode and output electrode like that ofFIG. 1.

FIGS. 6A and 6B show an alternative, preferred embodiment of a nanotubeswitching element in cross section view and plan view. This embodimenthas a control electrode 601 similar to the other embodiments but locatedmore centrally. It has output nodes 608 and 610 located on either sideof the control electrode 601. Each of the output nodes 608 and 610includes two electrodes on opposite sides of the nanotube channelelement similarly to that described before. Each of the electrodes of agiven node is tied to the other. This is shown in FIG. 6B by the ‘X’indication. Like some of the earlier embodiments, the gap dimensionbetween the control electrode and channel element is different than thegap dimension between the output electrode and channel element.

If the output nodes 608 and 610 are tied together, then the embodimentessentially has redundant output electrodes and has lower resistancefrom parallel outputs. Alternatively, the output nodes may remainindependent (as shown in FIG. 6B where they are not shown coupled), andin this case, the element may operate as an analog transfer device.

FIGS. 7A and 7B show an alternative, preferred embodiment of a nanotubeswitching element in cross section view and plan view. This embodimenthas an output node 702 located more centrally. It has two separatecontrol electrodes 712 and 714 (similar to those described before)located on either side of the output node 702. The output node includetwo pairs of output electrodes. One pair of output electrodes 716 a,b islocated on the left of a central pinning post 720 and a second pair ofoutput electrodes 718 a,b is located on the right of post 720. Theelectrodes of each pair are tied to the other as indicated by the ‘X’ inFIG. 7B. Thus electrode 716 a is tied to 716 b, and 718 a is tied to 718b. The pairs in turn may be tied to each other as well, depending on theintended usage. Likewise, the control electrodes 712 and 714 may be tiedtogether. In this fashion the control electrodes will either allow thechannel element 103 to float or to mechanically and electrically contactboth electrodes 716 a and 718 a. Alternatively, the control electrodesmay be operated with independent signals. The pinning post 720 providesmore support for the channel element 103 so the extended length of thechannel element is effectively reduced.

FIGS. 8A and 8B show a minimum arrangement in which the channel element103 is formed of a single nanotube, and in which the control and outputelectrodes are likewise formed of nanotubes. As explained herein,preferred embodiments utilize porous nanofabric to make nanotube channelelements 103. As described in the incorporated references, the fabric isformed and lithographically defined and patterned to create ribbon-likestructures which may be arranged horizontally (as shown herein) orvertically (as described in incorporated references). As the minimumlithographic dimensions continue to shrink with improving technology andas the fabrics remain highly porous, a given channel element may beformed to have relatively few nanotubes with a theoretical minimum beingone, as shown in FIG. 8A. Likewise the electrodes may be made fromnanotubes or nanotube ribbons, if desired, as discussed in theincorporated references. Alternatively, the arrangement of FIG. 8 a maybe made with other manufacturing techniques that do not rely onphotolithographic limits, such as disclosed in some of the incorporatedpatent references. The embodiment of FIG. 8 therefore has theoreticallyminimum sized channel element 103. It also uses nanotubes as the controlelectrode and output electrode, providing nanotube-to-nanotube contactin the case of the output electrode when a channel is formed.

The nanotube switching elements 100 may be used to create largercircuits such as Boolean logic circuits. For example, a resistive loadmay be used on the output node 102 to form an inverter (not shown).Alternatively, the switching devices 100 may also be used as a form ofcomplementary logic, in which the switches 100 are used as “loads” orpull-up devices. Complementary logic formed using switches 100 will notconduct DC current between power supply and ground.

For example, as will be explained below, NOR and NOT circuits may bebuilt using the nanotube switching elements. Each of these Booleanfunctions includes an inversion aspect, e.g., inverting the logic valueof the input in the case of NOT function. NORs and NOTs (and NANDs)provide a fundamental building block from which any Boolean function maybe created and enable the creation of an entire logic family.

FIGS. 9-11C show the layout and operation of an exemplary invertercircuit. FIGS. 12A-16C show the layout and operation of an exemplary NORcircuit.

FIG. 9A shows an inverter circuit 900 of a preferred embodiment. Thecircuit 900 implements a Boolean NOT functional transformation of theinput signal received on terminal A and produces the output on terminal0. The circuit is depicted logically in FIG. 9B, and its truth tabledescription of operation is provided in FIG. 9C.

As shown in the layout view of FIG. 9A, the circuit 900 includes twonanotube switching elements 902 and 904. These switching elements aresimilar to those of FIG. 3 or 5 in that each includes two signalelectrodes, as shown. An input signal is received on input terminal A,which is connected via trace 906 to respective control electrodes ofnanotube switching elements 902 and 904. The signal electrode ofnanotube switching element 902 is tied to reference signal Vdd, and thesignal electrode of nanotube switching element 904 is tied to referencesignal ground. (Notice that these switching elements have the referencesignals connected to signal electrodes that are nearer the outputelectrode, but the reference signals could alternatively, or inaddition, be connected to the other signal electrode of the switchingelement.) The output electrode of each output node is tied together (asdescribed previously) and as depicted with the ‘X’ notation in thefigure. The output node of each of the nanotube switching elements 902and 904 is tied to the other output node via trace 908 which is alsoconnected to output terminal 0.

FIGS. 10A-C depict the operation of circuit 900 when the input terminalhas a logically false or 0 value which in this arrangement correspondsto a signal substantially equal to ground. (Notice the arrow of FIG. 10Cidentifying which row of the truth table is being depicted.) As can beseen in the figure, the nanotube switching element 902 has a logical 0on the control electrode and Vdd on the signal electrode. The thicklined, but empty circle shown on the control node of switching element902 is used to depict that the control electrode has activated thechannel formation, and that the nanotube channel is in mechanical (butnot electrical) contact with the control electrode. The filled circleshown on the output electrode (over the area having the nanotube channelelement) is used to depict that the nanotube channel element is inmechanical and electrical contact with an output electrode. The ‘X’notation is again used to show that elements are tied together. Asexplained before in connection with the description of the switchingelement of FIGS. 1A-B, having a ground on the control electrode and Vddon the signal electrode creates electrostatic forces to cause thechannel element to form a channel with the output electrode. Thischannel formation is shown via thick lined, but empty circle shown onthe control node and the filled circle shown on the output electrode.Because the channel is formed, the signal Vdd on the signal electrodecan be transferred (via the channel) to the output node and in turn tothe trace 908 and the output terminal 0. On the other hand the nanotubeswitching element 904 has a logical 0 on the control node and ground onthe signal electrode. No electrostatic forces are generated to form thechannel for that switching element and consequently no channel is formedand the output node of element 904 floats. In this instance, the outputnode is at Vdd because of the operation of switching element 902. Eventhough the output node of switching element 904 is at Vdd and thechannel element is at logical 0, the channel element is not deflectedbecause of the operation of the isolation structure describedpreviously; that is, the floating output does not cause the deflectionof the nanotube channel element of switching element 904.

FIGS. 11A-C depict the operation of circuit 900 when the input terminalhas a logically true or 1 value. The operation is analogous to thatabove. In this instance the switching element 902 floats, and theelement 904 forms a channel. The channel causes the signal on the signalelectrode (ground) to transfer to the output node and in turn to thetrace 908 and the output terminal 0.

FIG. 12A shows a NOR circuit 1200 of a preferred embodiment. The circuit1200 implements a Boolean NOR functional transformation of the inputsignals received on terminals A and B and produces the output onterminal 0. The circuit is depicted logically in FIG. 12B, and its truthtable description of operation is provided in FIG. 12C.

As shown in the layout view of FIG. 12A, the circuit 1200 includes fournanotube switching elements 1202, 1204, 1206, and 1208. The signalelectrodes are connected as labeled to Vdd and ground. Notice in thisexample that the signal electrode of switching element 1204 is connectedto the output electrode of element 1202.

FIGS. 13A through 16A iterate through the various combinations of inputsignals, i.e., rows of the truth table. They use the same notationincluding filled circles to show electrical and mechanical contact andthick line unfilled circles to show mechanical (but not electrical)contact used before in connection with the inverter (or NOT) circuit.Each figure therefore shows when a given channel has been activated(thick lined, unfilled circle) and when a channel is formed to theoutput (filled circle). Thus one can determine which switching elementhas a channel formed and which has a floating channel from directinspection of the figures to see how the circuit operates for all inputcombinations.

FIGS. 17A and 17B illustrate a ring oscillator 1700. Thousands of ringoscillators over a chip area may be used to test and characterize atechnology—a great line monitor. Such ring oscillators with varyingnanotube fabric structures can be used to debug a CMOS process that usesnanotube fabrics. The ring oscillator line monitor gives the performanceof nanotube fabrics, impacts of nanotube fabrics due to the integratedcircuit process. It can characterize the performance of a logic familyas well. The oscillator is triggered by a start/stop input 1702 and theoutput 1704 is monitored. When the start/stop voltage goes from high tolow, the output oscillates, as shown in FIG. 17B. These oscillations aremonitored. When the start/stop input goes to a high voltage, theoscillations stop. These line monitors can be used to monitor thevoltage output levels, speed, power supply voltage sensitivity, etc. asa function of temperature, number of cycles, etc. Ring oscillators canbe packaged and subjected to aggressive environments tests and monitoredwhile operating. It can be tested in other harsh environments.

A ring oscillator using an odd number of stages is shown in FIGS. 17Aand 17B. The input stage 1706 is a two input NOR, all other stages areinverters. In preferred embodiments, the ring oscillator is formed usingnanotube switching elements in complimentary form, as described above inconnection with the NOT and NOR circuits of FIGS. 9 and 12. Tabs at each(or select) circuit stages can be used to probe individual stages forfailure analysis purposes. The ring oscillator can be tapped at morethan one point to switch a non-volatile storage nanotube-based device ONto OFF and OFF to ON as a stress test. The ring oscillator excercisesnanotube-based devices. The nanotube-based logic family excels in harshenvironments. There are no semiconductor junctions, hence leakage ismuch lower than for transistors, diodes, etc. The nanotube-based logiccan be used in burn-in and other harsh chambers to monitor theperformance of devices, such as FETs and bipolar devices that fail afterextended exposure to harsh environments.

The nanotube switching elements may be designed to ensure that channelformation is broken faster than channel formation is formed. In thisfashion, inverter circuits and the like may be operated to reduce shootthrough current for the temporary time when both switching elementsmight otherwise have channels formed. One way to address this is to sizethe device so that the electrical contact release forces are greaterthan the forces for channel formation.

The nanofabric switching elements of certain embodiments are generallyvolatile switches, i.e., after contacting an electrode, the nanofabricdoes not stay in contact with that contacted electrode when electricalstimulus is interrupted.

Under some embodiments, the nanotube-based switching elements may beconstructed physically over existing bipolar and MOS electronic devicesto integrate nanotube logic with existing electronic circuitry. Otherembodiments create digital logic on substrates other than silicon tointegrate digital logic circuits in objects not suited to conventionaldigital circuit integration. Some embodiments do not necessarily draw DCcurrent and may only dissipate power when they switch.

A nanofabric or ribbon has been shown to substantially conform to asurface, such as a surface of an article on a semiconductor substrate. Afabric of nanotubes may be constructed by any appropriate means,including, but not limited to spin coating, direct growth on a suitablesubstrate or other application. The fabric will be horizontally orientedwhen the surface of the substrate that receives the fabric ishorizontally oriented. The present inventors have appreciated thatdevices such as electromechanical switches can be constructed usingnanofabrics which have conformed to a surface which is substantiallyperpendicular to a semiconductor substrate (vertically-oriented) andthat such devices can be used as vertically oriented switches in aplethora of applications. Fabrication techniques to develop suchhorizontally- and vertically-disposed fabrics and devices composed ofnanotube fabrics which comprise redundant conducting nanotubes may becreated via CVD, or by room temperature operations as described hereinand described in the patent references incorporated herein. Suchfabrication techniques include the ability to form said switches for usein many different articles having relatively short spans of suspendednanofabric articles. In some embodiments, this allows smaller devicedimensions and higher strains in the nanofabric articles, as well aslower electrical resistances. Such articles may be adapted or modifiedto perform logic functions or be part of a scheme involving logicalfunctionality.

While the nanotube switching element 100 is shown with a lateral(horizontal) orientation, the device may also be fabricated with avertical orientation, such as on a sidewall of a trench structure. Also,the device may be at any angle, such as forty-five degrees, for example.

While the nanotube switching element 100 is describe with the electrodes102 a,b electrically connected, in other embodiments the electrodes maybe unconnected and at different voltages (i.e., separately driven tosufficient voltages—perhaps with different control). Also, the controlelectrode 101 may be above the nanotube device instead of below thenanotube. And the channel may transfer signals to an output node otherthan through mechanical and electrical contact, e.g., capacitivecoupling.

The inventors expect this logic to be lower power than CMOS, much lessleaky, extreme environment tolerant, etc. It is also very robust becausethere is no increased leakage with temperature, making it very useful inhot or cold environments such as the heat of engines, etc., as well inordinary electronics whose operating temperatures meets or exceeds thespecifications of the current state of the art electronics capabilities.The nanotube-based logic can be incorporated into a line of productsthat do not use transistors.

The devices and articles shown in the preceding embodiments are givenfor illustrative purposes only, and other techniques may be used toproduce the same or equivalents thereof. Furthermore, the articles shownmay be substituted with other types of materials and geometries in yetother embodiments. For example, rather than using metallic electrodes,some embodiments of the present invention may employ nanotubes. In fact,devices comprising nanotube and nanofabric articles in place of theelectrodes shown above can be constructed as well.

The inventors envision additional configurations of volatile andnonvolatile or mixed nanoelectromechanical designs depending upon thespecific application, speed, power requirements and density desired.Additionally the inventors foresee the use of multiwalled carbonnanotubes, nanowires, or mixtures of single-walled carbon nanotubes andnanowires as the switching element of contact points within the switch.As the technology node decreases in size from 90 nm to 65 nm and belowdown to the size of individual nanotubes or nanowires the inventorsforesee adapting the basic electromechanical switching elements andtheir operation to a generation of nanoscale devices with scaleableperformance characteristics concomitant with such size reduction.

The material used in the fabrication of the electrodes and contacts usedin the nanotube switches is dependent upon the specific application,i.e. there is no specific metal necessary for the operation of thepresent invention.

Nanotubes can be functionalized with planar conjugated hydrocarbons suchas pyrenes which may then aid in enhancing the internal adhesion betweennanotubes within the ribbons. The surface of the nanotubes can bederivatized to create a more hydrophobic or hydrophilic environment topromote better adhesion of the nanotube fabric to the underlyingelectrode surface. Specifically, functionalization of a wafer/substratesurface involves “derivitizing” the surface of the substrate. Forexample, one could chemically convert a hydrophilic to hydrophobic stateor provide functional groups such as amines, carboxylic acids, thiols orsulphonates to alter the surface characteristics of the substrate.Functionalization may include the optional primary step of oxidizing orashing the substrate in oxygen plasma to remove carbon and otherimpurities from the substrate surface and to provide a uniformlyreactive, oxidized surface which is then reacted with a silane. One suchpolymer that may be used is 3-aminopropyltriethoxysilane (APTS). Thesubstrate surface may be derivitized prior to application of a nanotubefabric.

While single walled carbon nanotubes are preferred, multi-walled carbonnanotubes may be used. Also nanotubes may be used in conjunction withnanowires. Nanowires as mentioned herein is meant to mean singlenanowires, aggregates of non-woven nanowires, nanoclusters, nanowiresentangled with nanotubes comprising a nanofabric, mattes of nanowires,etc. The invention relates to the generation of nanoscopic conductiveelements used for any electronic application.

The following patent reference refer to various techniques for creatingnanotube fabric articles and switches and are assigned to the assigneeof this application. Each is hereby incorporated by reference in theirentirety.

-   -   U.S. Pat. Apl. Ser. No. 10/341,005, filed on Jan. 13, 2003,        entitled Methods of Making Carbon Nanotube Films, Layers,        Fabrics, Ribbons, Elements and Articles;    -   U.S. Pat. Apl. Ser. No. 09/915,093, filed on Jul. 25, 2001,        entitled Electromechanical Memory Array Using Nanotube Ribbons        and Method for Making Same;    -   U.S. Pat. Api. Ser. No. 10/033,032, filed on Dec. 28, 2001,        entitled Methods of Making Electromechanical Three-Trace        Junction Devices;    -   U.S. Pat. Apl. Ser. No. 10/033,323, filed on Dec. 28, 2001,        entitled Electromechanical Three-Trace Junction Devices;    -   U.S. Pat. Apl. Ser. No. 10/128,117, filed on Apr. 23, 2002,        entitled Methods of NT Films and Articles;    -   U.S. Pat. Apl. Ser. No. 10/341,055, filed Jan. 13, 2003,        entitled Methods of Using Thin Metal Layers to Make Carbon        Nanotube Films, Layers, Fabrics, Ribbons, Elements and Articles;    -   U.S. Pat. Apl. Ser. No. 10/341,054, filed Jan. 13, 2003,        entitled Methods of Using Pre-formed Nanotubes to Make Carbon        Nanotube Films, Layers, Fabrics, Ribbons, Elements and Articles;    -   U.S. Pat. Apl. Ser. No. 10/341,130, filed Jan. 13, 2003,        entitled Carbon Nanotube Films, Layers, Fabrics, Ribbons,        Elements and Articles;    -   U.S. Pat. Apl., Ser. No. 10/776,059, filed Feb. 11, 2004,        entitled Devices Having Horizontally-Disposed Nanofabric        Articles and Methods of Making The Same; and    -   U.S. Pat. Apl., Ser. No. 10/776,572, filed Feb. 11, 2004,        entitled Devices Having Vertically-Disposed Nanofabric Articles        and Methods of Making the Same.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of the equivalency ofthe claims are therefore intended to be embraced therein.

1. An isolation structure for a deflectable nanotube element,comprising: a pair of electrodes disposed on opposite sides of ananotube element, at least one of said pair of electrodes being anoutput terminal, said pair producing substantially the same but opposingelectrostatic forces on the nanotube element.
 2. The structure of claim1 wherein said electrodes are in low resistance electricalcommunication.